Method for the manufacture of hard surface layer on the automatic freight car coupler part

ABSTRACT

The invention relates to the field of heat treatment of metals and may be used for hardening the railway transport automatic coupler parts. The hardening method includes induction heating of the automatic coupler and its subsequent cooling. The induction heating is performed within the automatic coupler part working surface area. The heated surface is cooled by water fed through openings in the coil body.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority from Russian Patent No. 2 673 437 C1, filed Mar. 22, 2018, the disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to the field of metallurgy and may be used for heat treatment of the railway rolling stock automatic coupler parts to manufacture a hard layer on the wearing part working surfaces.

BACKGROUND OF THE INVENTION

A method is disclosed for the manufacture of a hard surface layer by multirun build-up welding on the working surfaces of the railway car automatic coupling device parts to ensure zero ruptures of the welded layer at the edges of the said working surfaces (RU 57226 U1, publ. Oct. 10, 2006). Known process contains two embodiments wherein the automatic coupling device working surfaces are initially decreased by the height of welded layer and then are built up with wear-resistant wire through several runs. According to one the embodiments, edging beads are implemented at the edges of working surfaces and made of wire with hardness less than the hardness of wire used to make the main build-up weld. According to the other embodiment, ridges are cast integral with the part body and have a hardness less than the hardness of wire used to make the main build-up weld.

When implementing this method there is a need for local change of mold shapes, in which the part will be manufactured. If after applying a build-up weld, the part geometry does not comply with the documentation requirements, additional machining may be required to obtain the desired welded layer configuration and dimensions. In addition, it is necessary to acquire additional materials (wire) to perform the build-up welding.

A method is also disclosed for heat treatment of molded parts of a coupler, used for automatic coupling of the railway rolling stock, to obtain increased hardness and cyclic life of the automatic coupler part material (RU 2415182 C1, publ. Mar. 27, 2011). Known method of post-restoration heat treatment process of the automatic coupler parts, selected as the closest prior art, includes the high-frequency (HF) induction heating of the automatic coupler part at 890-940° C. for 5-30 minutes and subsequent cooling of the automatic coupler part, placed in a hardening tank, with closed-system water flow for 0.4-2.5 minutes. Equipment for the implementation of this method may include: power coil for heating the automatic coupler part, power supply, hardening tank, quench, matching transformer block, pump.

This method enables to heat treatment and hardness increases of the entire surface of the automatic coupler part being restored as a whole, however, it does not allow manufacturing of a hard layer on the distinct working surface of the automatic coupler part that is most prone to wear, in particular, on the pulling surface of the large and small teeth or the lock engagement surface.

BRIEF SUMMARY OF THE INVENTION

The technical result provided by the invention is the increased hardness of the freight car automatic coupler part working surfaces most prone to wear, while ensuring preservation of the initial configuration of working surfaces, including the edges, and increased durability of the freight car automatic coupler part.

This technical result is achieved by the fact that the method for the manufacture of hard surface layer on the freight car automatic coupler part includes induction heating of the part surface and cooling of the heated surface with a water feed, while the induction heating, as distinct from the closest prior art, is performed with power coil by progressive feed method within the automatic coupler part working surface zone, excluding the working surface edge, the part working surface is pre-scanned in order to plot the coil motion trajectory within the induction heating zone, the coil is moved over the part working surface using automatic control within the induction heating zone, and the cooling is performed when the coil is moved, by water fed to the heated surface through openings made in the power coil body.

As the power coil a square ferrite copper tube can be used.

In specific implementations, the power coil is moved at a constant distance of 1 mm to 3 mm from the part working surface.

Preferentially, the width of the part working surface edge is 5 mm to 10 mm.

The openings in the power coil body may be implemented at an angle to the power coil bottom to ensure an inclined direction of the water feed to the heated surface coincident with the direction of the power coil motion.

The part working surface on which the induction heating is performed for the purpose of manufacturing a hard surface layer can be the pulling surface of the large tooth or pulling surface of the small tooth of the automatic coupler body.

The high-frequency progressive induction heating method allows performance of heating and creation of a hard layer on specific surfaces of the part, namely on the working surfaces most prone to wear during the freight car automatic coupler operation. The cooling of heated surface by water fed to this surface while the coil is moved allows performance of the cooling stage shortly after the induction heating stage thereby excluding the dwell stage while ensuring the creation of a hard layer on the part working surface without heating through the part. The induction heating within the working surface zone of the automatic coupler part, excluding the working surface edge, does not affect the initial configuration of the part. The working surface edge not subject to the induction heating preserves the initial hardness of the surface layer thereby reducing the probability of the brittle fracture of the edge during the automatic coupler operation. The proposed stage sequencing ensures increased resistance to wear of the automatic coupler part working surface, increased durability, and increased interrepair life of the automatic coupler.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be explained by the drawings showing:

FIG. 1: position of the power coil over the pulling surface of the automatic coupler body large tooth, axonometric projection;

FIG. 2: position of the power coil over the pulling surface of the automatic coupler body small tooth, axonometric projection;

FIG. 3: automatic coupler body large tooth with induction heating zone, fragmentary cross-sectional view;

FIG. 4: automatic coupler body small tooth with induction heating zone, fragmentary cross-sectional view;

FIG. 5: hardness of a structure at 99.9% martensite as a function of carbon content in steel.

DETAILED DESCRIPTION

The proposed invention allows creation of a hard surface layer on such working surfaces of the automatic coupler body 1 as working surface 2.1 of large tooth 2 (FIG. 1) and working surface 3.1 of small tooth 3 (FIG. 2). Power coil 4, which can have different configurations of its part that faces the working surface 2.1 or 3.1, is implemented with length L

3 or length L_(M3), respectively.

Induction heating zone 2.1.1 on large tooth 2 of the automatic coupler body 1 (FIG. 3) has width S

₃, depth h

₃ and is located at a distance from the end of large tooth 2 corresponding to width _(S)

₃ of edge 2.1.2.

Induction heating zone 3.1.1 on small tooth 3 of the automatic coupler body 1 (FIG. 4) has width S_(M3), depth h_(M3) and is located at a distance from the end of small tooth 3 corresponding to width _(SM3) of edge 3.1.2.

Power coil 4 is positioned in such a way that its section with length L that faces the part working surface is parallel with the short side of working surface 2.1 or 3.1. In addition, the value of said length L does not exceed the value of width S of the respective induction heating zone in order to exclude induction heating of the working surface edge. Width _(S)

₃ and _(SM3) of edges 2.1.2 and 3.1.2 is 5 to 10 mm, which is determined by the requirement to preserve the working surface contour configuration. With edge width less than 5 mm an increased likelihood exists of chipping off the edges due to operating loads; with edge width more than 10 mm the area of induction heating zone with a hard surface layer is decreased.

The equipment for the implementation of proposed method comprises electrical and mechanical component, including HF power coil, scanning device, power coil position and motion automatic control system (ACS), and high frequency power generator. As the power coil, in particular, a square ferrite copper tube is used. In the copper tube body through holes are implemented so that the power coil can perform the function of cooling device.

Before induction heating (HF hardening) of an automatic coupler part is performed, the part working surface is scanned in order to determine the working surface geometry. The scanning results are sent to the ACS to plot the coil motion trajectory over the part working surface.

To perform the proposed process, power coil 4 is positioned over pulling surface 2.1 of large tooth 2 of the automatic coupler body 1 (FIG. 1) or over pulling surface 3.1 of small tooth 3 of the automatic coupler body 1 (FIG. 2) and the power coil 4 is activated. Power coil 4 moves with a constant speed, in the direction of three axes set by the ACS while maintaining a constant distance over the working surface, and following individual geometry of the part working surface, including its curved sections.

For the induction heating zone cooling when power coil 4 is moved, water is fed to the heated surface through openings made in power coil 4 body bottom. In addition, the openings may be implemented at an angle to the power coil bottom to ensure an inclined direction of the water feed to the heated surface coincident with the direction of the power coil motion.

The surface layer hardness obtained by this method is within 40.5-50.0 HRC range. This hardness range is achieved by obtaining, as a result of hardening, a layer with martensite structure with carbon content of 0.17-0.25% (FIG. 7).

After performing the HF surface hardening low-temperature, tempering is performed at 180-250° C. for residual stress relief.

The distinctiveness of each separate surface that exists due to rather high dimensional tolerances is taken into account by the ACS and by pre-scanning of each surface, before the induction heating, to plot the power coil motion trajectory.

For different versions of 20GL steel within the grade composition according to GOST 22703 “Molded Parts of Coupling and Automatic Coupling Devices of Railway Rolling Stock: General Specifications” computer-based estimates were made taking into account the metal rate of heating and the metal initial state before HF hardening after volume hardening and tempering. The induction heating temperature range at a depth of h=3 mm is 880-910° C. and is governed by obtaining homogeneous austenite. The induction heating temperature on the part surface is between 910 to 1150° C. The temperature upper value of 1150° C. is governed by the fact that above this temperature, excessive austenite grain growth occurs: more than average nominal diameter of 55 mcm (corresponds to number 5 according to GOST 5

39 “Steels and Alloys: Methods of Detection and Determination of Grain Size”). The power coil movement speed is 1.5-3 mm/s. The distance between the power coil and the part working surface is 1 to 3 mm. These ranges of power coil movement speed and distance between the power coil and the part working surface are selected to ensure the above induction heating temperature ranges of the part on its working surface and at a depth ‘h’ of no more than 3 mm. 

1-7. (canceled)
 8. A method of creating a hard surface layer comprising the steps of: induction heating a section of a surface of a metallic part by moving a power coil proximate to the section of the surface; cooling the section that was heated with liquid emitted from a feed that is disposed proximate to the power coil and moves in concert with the power coil.
 9. The method of claim 8, further comprising the steps of: scanning the section of the surface of the metallic part with a scanning device prior to the induction heating step; controlling the moving of the power coil and feed with an automatic control system that determines the moving at least in part based upon the scanning.
 10. The method of claim 8, wherein the power coil is moved at a constant distance of 1 mm to 3 mm from the section of the surface.
 11. The method of claim 8, wherein metallic part is a train car coupler and the section of the surface that is heated and cooled is a working surface of the coupler.
 12. The method of claim 11, wherein the working surface that is heated and cooled does not include the edge proximate to the working surface and that edge is 5 mm to 10 mm wide.
 13. The method of claim 11 where in the working surface is a pulling surface of a large tooth of the coupler.
 14. The method of claim 11 where in the working surface is a pulling surface of a small tooth of the coupler.
 15. The method of claim 8, wherein the power coil is a high frequency power coil.
 16. The method of claim 8, wherein the power coil is a ferrite copper tube.
 17. The method of claim 8, wherein the feed comprises openings in the power coil body.
 18. The method of claim 17, wherein the openings in the power coil body are at an angle to a bottom of the power coil to direct the liquid towards the surface heated by the power coil.
 19. The method of claim 8, wherein the induction heating temperature at the surface is in the range between 910 degrees Celsius and 1150 degrees Celsius.
 20. The method of claim 8, wherein the induction heating temperature at a depth of 3 mm is in the range between 880 degrees Celsius and 910 degrees Celsius.
 21. An apparatus for creating a hard surface layer comprising: a movable power coil comprising a tube that includes holes, wherein the power coil is capable of heating a surface and the holes are capable of feeding a liquid to the surface that was heated; an automatic control system capable of scanning the surface and directing motion of the power coil over the surface based upon the scanning.
 22. The apparatus of claim 21, wherein openings of the holes are angled to direct the liquid towards the heated surface.
 23. An apparatus of claim 21, wherein the power coil is a square ferrite copper tube.
 24. A train car coupler comprising: a large tooth and a small tooth coupled to one another; wherein a section of a working surface of at least one of the large tooth or the small tooth is hardened to a range of 40.5 HRC to 50.0 HRC.
 25. The train car coupler part of claim 24, where the section of the working surface that is hardened comprises a layer with a martensite structure with carbon content in the range of 0.17% to 0.25%.
 26. The train car coupler part of claim 24, where in the hardened section of the working surface does not include the edge of the working surface.
 27. The train car coupler of claim 26, wherein a width of the edge is in the range of 5 mm to 10 mm. 